The invention relates to an electrical parking brake system for a commercial or utility vehicle and to a method for operating the electrical parking brake system.
In commercial or utility vehicles, electrical parking brake systems, which have to be integrated into the pneumatic brake system of the vehicle, are being used to an increasing degree. The particular feature of electrical parking brake systems is that a handbrake valve is no longer provided to operate them but rather an electrical switch which transmits signals to the electronic control unit of the parking brake system. The electronic control unit then actuates one or more valves as a function of these signals in order to in this way ventilate or vent the spring-type brake cylinders of the parking brake system, that is to say to release or apply the parking brake system.
With respect to ventilation, that is to say the release of the parking brake system, it is important to comply with certain safety criteria. In particular, the parking brake must never be opened if there is still sufficient pressure in the service brake system to activate the service brake. At least what is referred to as the auxiliary brake pressure must be present, the auxiliary brake pressure being a pressure below the normal service brake pressure which is, however, already sufficient to brake the motor vehicle.
In particular, in some countries in northern Europe there are further safety regulations which apply. These regulations require what is referred to as the “Northland Park Brake Function”. This ensures that the parking brake can be released only if the driver is in the driver's cab. This is self-evident under normal conditions, that is to say when there is sufficient pressure in the brake system, because the activation element for releasing the parking brake is located in the driver's cab so that the driver must necessarily be present in the driver's cab, as a result of which, when the parking brake is released, he is also able to bring the vehicle to a standstill at any time by activating the service brake. However, a hazardous situation may occur if the driver starts the vehicle engine when the brake system is pressureless, and therefore only then does he activate the build-up of pressure through the operation of the compressor. If the driver opens the compressed air path to the spring-type brake cylinders at this time, this means that the parking brake will not yet be released owing to inadequate pressure. The vehicle is therefore stationary and the driver could assume incorrectly that overall the situation is safe. If the driver then leaves the driver's cab, in order, for example, to clear away ice from an iced-up windshield, this may lead to a situation in which the pressure becomes sufficient to release the parking brake precisely when the driver is no longer located in the driver's cab. This results in the vehicle rolling away and possibly even rolling over the driver who is concerned with cleaning the windows.
DE 103 41 723 B4 has already proposed a concept for avoiding this problem. This concept is based on the fact that the control unit of an air-treatment system monitors signals which are characteristic of the presence of the driver in the driver's cab. If these signals are not received, the compressed-air supply of the handbrake valve, and therefore also of the spring-type brake cylinders, is shut off. The compressed-air supply of the parking brake is not enabled by the air-treatment system until the driver is present and there is sufficient pressure available for the auxiliary braking effect. Shutting off or enabling of the supply of the air-treatment system is carried out here in such a way that the function of an overflow valve, which is assigned to the parking brake system, is influenced by ventilating or venting a control inlet of the overflow valve.
The invention is based on the object of implementing in a simplified fashion the “Northland Park Brake Function” described above.
This object is achieved by an electrical parking brake system for a utility vehicle, having a valve device which connects a compressed-air supply to a spring-type brake cylinder without intermediate connection of a handbrake valve, wherein in a first switched state the electrically actuable valve device ventilates (aerates) the spring-type brake cylinder, and in a second switched state the valve device vents (deaerates) the spring-type actuator. A pressure sensor is provided with which a compressed-air-supply-side pressure can be measured. An electronic control unit directly or indirectly actuates the valve device, registers a signal supplied by the pressure sensor and registers an indicator signal for the presence of a person in a driver's cab of the utility vehicle. The valve device can be transferred into its first switched state by the control unit only when the compressed-air-supply-side pressure exceeds a pressure threshold value and the indicator of the presence of a person in a driver's cab of the utility vehicle is present. In this way, a means of disabling the release of the parking brake on the supply side can be dispensed with so that, in particular, there is no need to provide a solenoid valve which is able, when necessary, to shut off an overflow valve which supplies the parking brake system. Instead, the valve device which is generally used for the pneumatic activation of the parking brake system is also directly influenced by the control device of the electrical parking brake system with respect to the shutting off of the ventilation of the parking brake cylinders. In this context, the electronic control unit of the parking brake system can perform a large number of tasks which are associated with the desired safety function, specifically the registration of the indicator signals for the presence, the registration of a pressure for ensuring the auxiliary braking effect, the logical combination of these conditions for the ventilation of the parking brake and the actuation of the valve device for the electrical parking brake system.
It is preferred that the electronic control unit is connected to an activation element which is arranged in the driver's cab of the utility vehicle. This connection of the activation element (also referred to as a manual control unit) to the control unit can be implemented by a direct electrical connection or by a signal bus. The manual control unit influences the operating sequences of the electrical parking brake as a function of the driver's request, but does so while decisively taking into account the safety functions in question.
It is advantageously provided that the valve device is a 3/2 way valve. Such a 3/2 way valve makes the necessary functionality available. Alternatively, it is also possible to provide that, instead of a 3/2 way valve, two 2/2 way valves which are arranged in parallel are provided. One of these two 2/2 way valves makes available, in the energized state, a connection to a supply, while the other 2/2 way valve makes available, in the energized state, a venting function. In the currentless state, the two 2/2 way valves are switched into the shut-off position by way of a spring.
It is advantageously possible to provide for the 3/2 way valve to be an electrically actuable solenoid valve. In particular, the electrically actuable solenoid valve can be a directly controlled 3/2 way solenoid valve which is arranged in the supply path and the venting path of the spring-type brake cylinders. If, in this case, the 3/2 way valve is replaced by two 2/2 way valves, one of these 2/2 way valves is responsible for ventilating the spring-type brake cylinder, and the other 2/2 way valve is responsible for venting the spring-type brake cylinder.
Furthermore, it is also possible for the 3/2 way valve to be an electrically activated, pilot-controlled valve. Basically, even with such pilot-control it is possible to adopt various ways of making available the basic functionality of an electrically activated, pilot-controlled 3/2 way valve. For example, the pilot-controlled solenoid valve may be configured as a 3/2 way valve or in the form of two 2/2 way valves, while the valve which is arranged in the ventilation path and in the venting path of the spring-type brake cylinders is still embodied as a 3/2 way valve. In this case, one of the 2/2 way valves serves to ventilate a control chamber of the 3/2 way valve, while the other 2/2 way solenoid valve vents the control chamber of the 3/2 way valve. It is particularly advantageous if the valve which is arranged in the venting path and the ventilation path of the spring-type brake cylinder can also implement a pressure-holding function in addition to the venting function and ventilation function. The pressure-holding function can be carried out, for example, by way of a slider valve which has an intermediate switched position between the venting switched position and the ventilating switched position, that is to say the slider valve is configured as a 3/3 way valve. The pressure-holding function can also be implemented on the basis of a 3/2 way relay valve, for example by use of pulse-width-modulated actuation.
It is possible to provide that the 3/2 way solenoid valve is bistable. In this way, a changeover between the two switched states of the valve device occurs only if corresponding control signals are output. Unintended release or application of the parking brake system is therefore avoided.
According to one aspect of the invention, there is provision that a 2/2 way valve is connected downstream of the 3/2 way valve. This increases the graduation capability of the parking brake system, in particular if a 2/2 way solenoid valve is arranged between a 3/2 way solenoid valve and the valve pilot-control chamber of a pilot-controlled valve.
It is possible to provide that the pressure sensor can be used to measure the pressure of the compressed air which is fed to the valve device. On the basis of this pressure it is possible to determine whether the necessary auxiliary braking effect is available.
Likewise it is possible to provide that the pressure sensor can be used to measure the pressure in one of the service brake circuits of the utility vehicle. This is advantageous, in particular, in the case of a serial supply of the parking brake system from the service brake circuits. In this case, there is preferably provision that the pressure threshold value is the closing pressure of an overflow valve which supplies the service brake circuit.
In a further embodiment of the present invention, the pressure sensor can be used to measure the pressure in a supply line which supplies both the service brake circuits and the valve device with compressed air. On the basis of a pressure measurement on such a central supply line it is also possible to assess whether the auxiliary braking effect can already be achieved.
It is possible to provide that the indicator signal for the presence of a person in a driver's cab of the utility vehicle can be transmitted to the electronic control unit when the driver's seat is occupied. According to a further embodiment, the indicator signal for the presence of a person in a driver's cab of the utility vehicle can be transmitted to the electronic control unit when the seat belt is put on.
The invention is also advantageously embodied in such a way that the indicator signal for the presence of a person in a driver's cab of the utility vehicle can be transmitted to the electronic control unit when the brake pedal and/or accelerator pedal are/is activated.
Furthermore, the valve device and/or the electronic control unit and/or the pressure sensor may be integrated into an air-treatment system. Even if the “Northland Park Brake Function” is no longer performed by the air-treatment system but rather by the electrical parking brake system, it can be equally advantageous to integrate components of the parking brake system into the electronic air-treatment system, in which case this includes, in particular, possible full integration, that is to say of the valve device, of the electronic control unit and of the necessary pressure sensors.
The invention also relates to a method for operating an electrical parking brake system for a utility vehicle, in which an electrically actuable valve device connects a compressed-air supply to a spring-type brake cylinder without intermediate connection of a handbrake valve. In a first switched state, the electrically actuable valve device ventilates the spring-type brake cylinder. In a second switched state, the electrically actuable valve device vents the spring-type actuator. A compressed-air-supply-side pressure is measured by a pressure sensor. An electronic control unit actuates the valve device and registers a signal which is supplied by the pressure sensor and an indicator of the presence of a person in a driver's cab of the utility vehicle, wherein the valve device is transferred into its first switched state only when the compressed-air-supply-side pressure exceeds a threshold value, and the indicator of the presence of a person in a driver's cab of the utility vehicle is present. In this way, the advantages and particular features of the electrical parking brake system according to the invention are also implemented in the method. This also applies in relation to the particularly preferred embodiments of the method according to the invention which are specified below.
The method is advantageously embodied in such a way that the electronic control unit registers signals from an activation element, which is arranged in the driver's cab of the utility vehicle.
It is preferred that the pressure sensor is used to measure the pressure of the compressed air which is fed to the valve device. Furthermore, it is possible to provide that the pressure sensor is used to measure the pressure in one of the service brake circuits of the utility vehicle.
The method can also be configured in such a way that the closing pressure of an overflow valve, which supplies the service brake circuit, is used as the pressure threshold value.
Furthermore, it is possible to provide that the pressure sensor is used to measure the pressure in a supply line which supplies both the service brake circuits and the valve device with compressed air.
The invention is particularly advantageously developed by a method such that the indicator signal for the presence of a person in a driver's cab of the utility vehicle is transmitted to the electronic control unit when the driver's seat is occupied. It is also possible for the indicator signal for the presence of a person in a driver's cab of the utility vehicle to be transmitted to the electronic control unit when the seat belt is put on.
According to a further embodiment of the method according to the invention, the indicator signal for the presence of a person in a driver's cab of the utility vehicle can be transmitted to the electronic control unit when the brake pedal and/or accelerator pedal are/is activated.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.